[LOG4J2-3418] Fix Log4j2CloudConfigLoggingSystem registration

This PR adds support for the `spring.factories` registration method of
the `Log4j2CloudConfigLoggingSystem` to replace the old Java system
properties injection method.

A Log4j 2.x `log4j2.disableCloudConfigLoggingSystem` property is added
to enable a choice between the `Log4j2CloudConfigLoggingSystem` and
`Log4j2LoggingSystem`.

log4j-spring-boot/src/main/java/org/apache/logging/log4j/spring/boot/Log4j2CloudConfigLoggingSystem.java

@@ -49,7 +49,10 @@
 import org.apache.logging.log4j.util.Strings;
 import org.springframework.boot.logging.LogFile;
 import org.springframework.boot.logging.LoggingInitializationContext;
+import org.springframework.boot.logging.LoggingSystem;
+import org.springframework.boot.logging.LoggingSystemFactory;
 import org.springframework.boot.logging.log4j2.Log4J2LoggingSystem;
+import org.springframework.core.annotation.Order;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ResourceUtils;
@@ -58,10 +61,17 @@
  * Override Spring's implementation of the Log4j 2 Logging System to properly support Spring Cloud Config.
  */
 public class Log4j2CloudConfigLoggingSystem extends Log4J2LoggingSystem {
-    private static final String HTTPS = "https";
+
+    /**
+     * Property that disables the usage of this {@link LoggingSystem}.
+     */
+    public static final String LOG4J2_DISABLE_CLOUD_CONFIG_LOGGING_SYSTEM = "log4j2.disableCloudConfigLoggingSystem";
+
     public static final String ENVIRONMENT_KEY = "SpringEnvironment";
+    private static final String HTTPS = "https";
     private static final String OVERRIDE_PARAM = "override";
     private static Logger LOGGER = StatusLogger.getLogger();
+    private static final int PRECEDENCE = 0;
 
     public Log4j2CloudConfigLoggingSystem(ClassLoader loader) {
         super(loader);
@@ -213,4 +223,18 @@ private ConfigurationSource getConfigurationSource(URL url) throws IOException,
     private LoggerContext getLoggerContext() {
         return (LoggerContext) LogManager.getContext(false);
     }
+
+    @Order(PRECEDENCE)
+    public static class Factory implements LoggingSystemFactory {
+
+        @Override
+        public LoggingSystem getLoggingSystem(ClassLoader classLoader) {
+            if (PropertiesUtil.getProperties().getBooleanProperty(LOG4J2_DISABLE_CLOUD_CONFIG_LOGGING_SYSTEM)) {
+                return null;
+            }
+            return new Log4j2CloudConfigLoggingSystem(classLoader);
+        }
+
+    }
+
 }

log4j-spring-boot/src/main/resources/log4j2.system.properties → log4j-spring-boot/src/main/resources/META-INF/spring.factories

@@ -14,4 +14,4 @@
 # See the license for the specific language governing permissions and
 # limitations under the license.
 #
-org.springframework.boot.logging.LoggingSystem=org.apache.logging.log4j.spring.boot.Log4j2CloudConfigLoggingSystem
+org.springframework.boot.logging.LoggingSystemFactory=org.apache.logging.log4j.spring.boot.Log4j2CloudConfigLoggingSystem.Factory

log4j-spring-boot/src/test/java/org/apache/logging/log4j/spring/boot/Log4j2CloudConfigLoggingSystemTest.java

@@ -19,23 +19,41 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.core.config.ConfigurationFactory;
 import org.apache.logging.log4j.spi.LoggerContext;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
+import org.junitpioneer.jupiter.SetSystemProperty;
+import org.springframework.boot.logging.LoggingSystem;
+import org.springframework.boot.logging.log4j2.Log4J2LoggingSystem;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.Arrays;
 import java.util.List;
 
-import static org.junit.Assert.assertTrue;
-
 public class Log4j2CloudConfigLoggingSystemTest {
 
     @Test
     public void getStandardConfigLocations() {
         String customLog4j2Location = "classpath:my_custom_log4j2.properties";
-        LoggerContext lc = LogManager.getContext(); // Initialize LogManager to here to prevent a failure trying to initialize it from StatusLogger.
+        LoggerContext lc = LogManager.getContext(); // Initialize LogManager to here to prevent a failure trying to
+                                                    // initialize it from StatusLogger.
         System.setProperty(ConfigurationFactory.CONFIGURATION_FILE_PROPERTY, customLog4j2Location);
-        Log4j2CloudConfigLoggingSystem cloudLoggingSystem = new Log4j2CloudConfigLoggingSystem(this.getClass().getClassLoader());
+        Log4j2CloudConfigLoggingSystem cloudLoggingSystem = new Log4j2CloudConfigLoggingSystem(
+                this.getClass().getClassLoader());
         List<String> standardConfigLocations = Arrays.asList(cloudLoggingSystem.getStandardConfigLocations());
         assertTrue(standardConfigLocations.contains(customLog4j2Location));
 
     }
+
+    @Test
+    @SetSystemProperty(key = Log4j2CloudConfigLoggingSystem.LOG4J2_DISABLE_CLOUD_CONFIG_LOGGING_SYSTEM, value = "true")
+    public void testUseLog4j2LoggingSystem() {
+        LoggingSystem loggingSystem = LoggingSystem.get(getClass().getClassLoader());
+        assertTrue(loggingSystem.getClass().equals(Log4J2LoggingSystem.class));
+    }
+
+    @Test
+    public void testLoggingSystemEnabled() {
+        LoggingSystem loggingSystem = LoggingSystem.get(getClass().getClassLoader());
+        assertTrue(loggingSystem.getClass().equals(Log4j2CloudConfigLoggingSystem.class));
+    }
 }

src/site/xdoc/manual/configuration.xml.vm

@@ -2878,6 +2878,12 @@ public class AwesomeTest {
       that advertises the same language(s) in order for scripting to be enabled. If no languages are specified, which is
       the default, the ScriptManager will not be installed.</td>
   </tr>
+    <tr>
+    <td><a name="log4j2.disableCloudConfigLoggingSystem"/>log4j2.disableCloudConfigLoggingSystem</td>
+    <td></td>
+    <td></td>
+    <td>Disables the usage of the Spring Boot <tt>Log4j2CloudConfigLoggingSystem</tt>. Defaults to <tt>false</tt>.</td>
+  </tr>
 </table>
 
         </subsection>